Digital projectors are typically constructed with spatial light modulators (e.g., digital mirror devices (DMDs) or liquid crystal displays (LCDs)) that have a fixed number of pixels, resulting in a fixed aspect ratio. However, video content is available in several different aspect ratios, and when video content is displayed using a light modulator with a mismatched aspect ratio, some of the pixels on the light modulator are not used. In other words, these pixels stay in their “off” state, and the light that would normally be used to illuminate these pixels is wasted.
By way of example, a typical digital projector has a DMD array with 1024×768 square pixels, providing an image with a 4:3 aspect ratio. HDTV content has a 16:9 aspect ratio (for example, 1920×1080). When HDTV content is scaled to fit by matching the width, approximately 25% of the pixels are not used. This also means that about 25% of the total lumens available are not used. Similar issues arise if the mirror array has a 16:9 aspect ratio, but the video content has a 4:3 aspect ratio. Another aspect ratio that is used in computer graphics displays is 5:4, resulting in other mismatches.
Thus, when digital projectors show video content that has a different aspect ratio than the light modulator used to form the image, some light is wasted. For light modulators and video content with mismatched aspect ratios, it would be desirable to be able to at least partially “recover” this lost light and increase the brightness of the image. It would also be desirable to be able to improve the apparent and/or actual contrast ratio between used and unused portions of a light modulator.